Hybrid window layer for photovoltaic cells

Abstract

A novel photovoltaic solar cell and method of making the same are disclosed. The solar cell includes: at least one absorber layer which could either be a lightly doped layer or an undoped layer, and at least a doped window-layers which comprise at least two sub-window-layers. The first sub-window-layer, which is next to the absorber-layer, is deposited to form desirable junction with the absorber-layer. The second sub-window-layer, which is next to the first sub-window-layer, but not in direct contact with the absorber-layer, is deposited in order to have transmission higher than the first-sub-window-layer.

1. A method for manufacturing a solar cell comprising the steps of:
 (i) providing a substrate; 
 (ii) depositing a layer of n-type semi-conductor on the substrate at a temperature that is one of 300° C. and sufficiently low to avoid damage or melting the substrate; 
 (iii) depositing an i-layer on the n-layer at a temperature that is one of 300° C. and sufficiently low to avoid melting or damaging the n-layer; 
 (iv) depositing a first sub-p-layer on the i-layer at a first temperature sufficiently high to form a good junction with the i-layer; and 
 (v) depositing a second sub-p-layer on the first sub-p-layer at a temperature lower than the first temperature at which the first sub-p-layer is deposited. 
 
     
     
       2. The method of  claim 1 , further including depositing a layer of a transparent conductive oxide on the second p-layer. 
     
     
       3. The method of  claim 2 , wherein a current collection layer is deposited onto the substrate prior to deposition of the n-layer onto the substrate. 
     
     
       4. The method of  claim 1 , wherein during the i-layer deposition an optimized GeH 4  to Si 2 H 6  ratio provides a Ge content suitable for forming a high efficiency single-junction solar cell. 
     
     
       5. The method of  claim 4 , wherein an optimized level of hydrogen dilution is used to form the i-layer. 
     
     
       6. The method of  claim 5 , wherein the substrate comprises glass or metal including aluminum, bismuth, iron, niobium, titanium or steel. 
     
     
       7. The method of  claim 1 , wherein the first and second sub-p-layers are deposited by a chemical vapor deposition process. 
     
     
       8. The method of  claim 7 , wherein the chemical vapor deposition process comprises plasma enhanced chemical vapor deposition. 
     
     
       9. The method of  claim 8 , in which the plasma enhanced chemical vapor deposition comprises radio frequency plasma enhanced chemical vapor deposition. 
     
     
       10. The method of  claim 9 , wherein the first and second p-layers amorphous silicon-containing material selected from the group consisting of hydrogenated amorphous silicon, hydrogenated amorphous carbon, and hydrogenated amorphous silicon germanium. 
     
     
       11. The method of  claim 10 , wherein the i-layer comprises hydrogenated amorphous silicon germanium having a bandgap ranging from about 1.4 e-V to 1.6 e-V and wherein the first and second sub p-layers comprise amorphous silicon with a bandgap of 1.4 e-V. 
     
     
       12. The method of  claim 11 , wherein the plasma enhanced chemical vapor deposition is by at least one of the following: cathodic direct current glow discharge, anodic direct current glow discharge, radio frequency glow discharge, very high frequency (VHF) glow discharge, alternate current glow discharge, or microwave glow discharge at a pressure ranging from about 0.5 to about 5 TORR with a dilution ratio of dilutant to feedstock (deposition gas) ranging from about 5:1 to about 200:1.